According to the present invention, in a gas injection type heat pump apparatus, the high-pressure side pressure of refrigeration cycle (21) is detected in a heating operation, and an upper limit value (BP) of an amount of air passing through an inside heat exchanger (14) is determined based on the detection value. The upper limit value (BP) and a set air amount (BO) set by an air amount switching lever (51) are compared. When the set air amount (BO) is larger than the upper limit value, the amount of the air passing through the inside heat exchanger is restricted within the upper limit value. In this way, the high-pressure side pressure increases, and an intermediate pressure in a gas-liquid separator also increases. Therefore, the gas injection amount can be increased, and a heating capacity can be effectively improved.